<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2016/1/31 0031
 * Time: 23:10
 */

$var  =  0 ;

 // Evaluates to true because $var is empty
 if (empty( $var )) {
     echo  '$var is either 0, empty, or not set at all'.'<br>' ;
 }

 // Evaluates as true because $var is set
 if (isset( $var )) {
     echo  '$var is set even though it is empty' ;
 }
 ?>